linux-kernel - [PATCH 14/16] block, bfq: convert to use request_queue->async

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Message-Id: <20250814033522.770575-15-yukuai1@huaweicloud.com>
Date: Thu, 14 Aug 2025 11:35:20 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	yukuai3@...wei.com,
	bvanassche@....org,
	nilay@...ux.ibm.com,
	hare@...e.de,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai1@...weicloud.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH 14/16] block, bfq: convert to use request_queue->async_depth

From: Yu Kuai <yukuai3@...wei.com>

The default limits is unchanged, and user can configure async_depth now.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/bfq-iosched.c | 43 +++++++++++++++++--------------------------
 1 file changed, 17 insertions(+), 26 deletions(-)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index de0dee255ccf..46520e50f584 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -7112,39 +7112,29 @@ void bfq_put_async_queues(struct bfq_data *bfqd, struct bfq_group *bfqg)
 static void bfq_depth_updated(struct request_queue *q)
 {
 	struct bfq_data *bfqd = q->elevator->elevator_data;
-	unsigned int nr_requests = q->nr_requests;
+	unsigned int async_depth = q->async_depth;
 
 	/*
-	 * In-word depths if no bfq_queue is being weight-raised:
-	 * leaving 25% of tags only for sync reads.
+	 * By default:
+	 *  - sync reads are not limited
+	 * If bfqq is not being weight-raised:
+	 *  - sync writes are limited to 75%(async depth default value)
+	 *  - async IO are limited to 50%
+	 * If bfqq is being weight-raised:
+	 *  - sync writes are limited to ~37%
+	 *  - async IO are limited to ~18
 	 *
-	 * In next formulas, right-shift the value
-	 * (1U<<bt->sb.shift), instead of computing directly
-	 * (1U<<(bt->sb.shift - something)), to be robust against
-	 * any possible value of bt->sb.shift, without having to
-	 * limit 'something'.
+	 * If request_queue->async_depth is updated by user, all limit are
+	 * updated relatively.
 	 */
-	/* no more than 50% of tags for async I/O */
-	bfqd->async_depths[0][0] = max(nr_requests >> 1, 1U);
-	/*
-	 * no more than 75% of tags for sync writes (25% extra tags
-	 * w.r.t. async I/O, to prevent async I/O from starving sync
-	 * writes)
-	 */
-	bfqd->async_depths[0][1] = max((nr_requests * 3) >> 2, 1U);
+	bfqd->async_depths[0][1] = async_depth;
+	bfqd->async_depths[0][0] = max(async_depth * 2 / 3, 1U);
+	bfqd->async_depths[1][1] = max(async_depth >> 1, 1U);
+	bfqd->async_depths[1][0] = max(async_depth >> 2, 1U);
 
 	/*
-	 * In-word depths in case some bfq_queue is being weight-
-	 * raised: leaving ~63% of tags for sync reads. This is the
-	 * highest percentage for which, in our tests, application
-	 * start-up times didn't suffer from any regression due to tag
-	 * shortage.
+	 * Due to cgroup qos, the allowed request for bfqq might be 1
 	 */
-	/* no more than ~18% of tags for async I/O */
-	bfqd->async_depths[1][0] = max((nr_requests * 3) >> 4, 1U);
-	/* no more than ~37% of tags for sync writes (~20% extra tags) */
-	bfqd->async_depths[1][1] = max((nr_requests * 6) >> 4, 1U);
-
 	blk_mq_set_min_shallow_depth(q, 1);
 }
 
@@ -7364,6 +7354,7 @@ static int bfq_init_queue(struct request_queue *q, struct elevator_queue *eq)
 	blk_queue_flag_set(QUEUE_FLAG_DISABLE_WBT_DEF, q);
 	wbt_disable_default(q->disk);
 	blk_stat_enable_accounting(q);
+	q->async_depth = (q->nr_requests * 3) >> 2;
 
 	return 0;
 
-- 
2.39.2